Earth’s Mass Extinctions, Past and Present

Earth has experienced five mass extinctions over its ~4.5 billion year history, with proposed causes ranging from extraterrestrial bolide impacts to massive flood volcanism. The fleeting time when human activities have significantly impacted the Earth system shows similarities with past episodes of mass extinctions. Current extinction rates are high, global environments are changing, the ocean is becoming more acidic and perhaps less oxygenated, and chemical pollution is widespread. Evidence suggests that a mass extinction, defined when Earth loses more than 75% of its total estimated species in a geologically short interval, may now be underway, driven by Homo sapiens.